This invention relates generally to radiopaque markers for endoscopic accessories and method of making same, and more particularly concerns thin walled medical device tubes, such as endoscopic accessory catheters, having radiopaque marker rings placed inside the tube.
Tubes formed of Teflon polymer, and other thin walled medical device tubes are not radiopaque. To make them visible on x-rays for film or fluoroscopy, a number of different approaches are commonly used. A first method of making these tubes radiopaque is to add metal powder filler to the plastic medical device tube during processing. These metal powders include barium, bismuth, lead, tungsten, and tantalum. The limitations of this method are that the metal powder decreases the mechanical integrity of the tubing polymer. Thus, there is a limit to the amount of metal powder filler that can be added. The amount of metal powder filler is also limited because it is not the only filler used. In thin walled tubes, this greatly limits the "radio density" or visibility under x-ray that can be achieved. This renders most small thin walled tubes invisible under x-ray, even with metal powder fillers. An additional disadvantage to this method is that the metal powder fillers may be highly toxic. Therefore, they can cause harm if any of it should remain in the patient.
A second method of making a device radiopaque is to include metal markers on the outside of the thin walled tube. These markers can be pre-formed metal rings or wire wrapped rings. Here, the markers on the outside of the tube have adequate radiopacity, i.e., they provide good visibility under x-ray. However, attachment to the tube can be a limitation. Additionally, the marker is typically a metal ring that has a larger diameter than the plastic medical device tube. Therefore, the marker creates a small bump, or enlarged region which may catch on body tissues or the inside of other devices which the tube may be slid through.
Many techniques have been developed to overcome this problem. A first such technique is to stretch the plastic tube, place the metal ring over the stretched plastic tube, and then allowing the plastic tube to recover to its original size (this recovery occurs by relaxation, heat, etc.), thereby fixing the metal ring in place over the plastic tubing. A second technique is to bond the metal ring in place by use of adhesives, etc. A third technique is to crimp the metal ring in place by using a swaging machine, crimping tool, or the like. A fourth technique is to cover the metal ring with a material which bonds to the plastic tube. This is particularly useful with balloon catheters. The sleeve or neck section of the balloon covers the ring. A fifth technique is to wrap a fine wire around the tube. Wire wrapping, however, has the same limitations as the pre-formed metal ring. Attachment is still difficult, and a bump or enlarged portion is still created at the location of the wire wrapping. In addition, the end of the wire is typically sharp and has to be finished to prevent harm to the patient. Also, the wire may have the tendency to "spring" back to its original, straight orientation, after winding onto the tube, causing it to enlarge or even come loose.
A third method of making a device radiopaque is to insert fine wire inside of an extra channel within the thin walled medical device tube. This method also has several disadvantages. Creating a separate channel in the plastic tubing makes it difficult to make small diameter tubing. Because the main channel, or lumen, of the tube is being used for the medical procedure, it must be as large as possible. Therefore, the separate channel must be made as small as possible. Because of the separate channel's small size, the radiopaque wire that passes through it is necessarily small as well. This limits the visibility of the wire under x-ray.
A fourth method is to add a radiopaque material into a matrix to add radiopacity. This can be done by placing powdered metal filler into an epoxy pre-polymer, and then applying the pre-polymer reactive mixture to the outside surface of the device, where it cures. This method also has several disadvantages. Firstly, the matrix decreases the mechanical integrity of the plastic tubing. Because of this, there is a limit to the size of the matrix that can be used, which, in turn, limits the visibility under x-ray that can be achieved. Additionally, the amount of metal powder filler that can be used is limited by the fact that other fillers will be used as well. This renders most small, thin wall tubes invisible under x-ray. Secondly, the use of a matrix increases the size of the tube because it creates a bump or enlarged region which may catch on body tissues or the inside of other devices.
All of these methods for making medical devices radiopaque have limitations when the device is Teflon polymer or Teflon polymer coated because Teflon polymer is not amenable to bonding.
Instead of the commonly used marker means, in the system of the present invention, a radiopaque marker ring is placed inside of the plastic medical tube. This has the advantage of creating a marker means that has good radiopacity and has a sound attachment of the marker means that becomes even more secure when the tube is stretched or bent. The dimensions of the radiopaque ring are such that other devices can slide through the tube without obstruction from the radiopaque ring. Placing the radiopaque ring inside of the tube in no way interferes with its function of locating the position of the ring during medical procedures, because it is just as radiopaque inside the tube as it is outside the tube.
Additionally, for an even more secure anchoring within the tube, the radiopaque ring can have one or both of its edges flared outward. This flared edge also allows for even easier passage of other devices through the ring. The radiopaque ring also serves other purposes. It can be used as an electrode within a medical device tube, which can be used, for example, as the catheter leads for heart stimulation and pacemakers. The radiopaque rings can also be used to provide support to the sides of the tube.
Additionally, it is possible to place more than one radiopaque ring within the medical device tube. It is also possible to insert the radiopaque rings in a tube that has more than one channel.
Accordingly, it is an object of the present invention to create a radiopaque marker with good radiopacity.
Yet another object of the invention is to provide a radiopaque marker in the form of a ring which will not cause a substantial protrusion on the outside of the tube in which it is located.
It is a further object of the present invention to create a radiopaque marker with good security of attachment.
It is still a further object of the present invention to create a radiopaque marker that is held even more securely when the tube is stretched or bent.
It is even still a further object of the present invention to create a radiopaque marker that does not cause a partial obstruction inside of the tube, and cannot be pushed out of the tube by a wire or other device moving through the tube.
It is even still a further object of the present invention to create a radiopaque marker with the above identified advantages, that can be easily constructed.